Measurements of the production cross-section for a Z boson in association with b -jets in proton-proton collisions at s
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Received: March 27, 2020 Accepted: June 15, 2020 Published: July 7, 2020
The ATLAS collaboration E-mail: [email protected] Abstract: This paper presents a measurement of the production cross-section of a Z √ boson in association with b-jets, in proton-proton collisions at s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb−1 . Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum pT > 20 GeV and rapidity |y| < 2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet. Keywords: Hadron-Hadron scattering (experiments) ArXiv ePrint: 2003.11960
Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP07(2020)044
JHEP07(2020)044
Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton √ collisions at s = 13 TeV with the ATLAS detector
Contents 1
2 The ATLAS detector
3
3 Data set and simulated event samples 3.1 Data set description 3.2 Simulated event samples for signal and background processes 3.3 Theoretical predictions
4 4 4 6
4 Event selection 4.1 Correction factors applied to simulation and corresponding uncertainties
9 11
5 Background estimation 5.1 Extraction of the cross-section for Z-boson production in association with light-jets and c-jets
12
6 Kinematic distributions
17
7 Correction to particle level
18
8 Uncertainties in the cross-section measurements
21
9 Results 9.1 Inclusive cross-sections 9.2 Differential cross-sections for Z + ≥ 1 b-jet 9.3 Differential cross-sections for Z + ≥ 2 b-jets
23 24 24 29
10 Conclusion
33
The ATLAS collaboration
41
1
14
Introduction
The measurement of the production rate of a Z boson in association with jets originating from b-quarks1 (Z + b-jets) in proton-proton (pp) collisions provides an important test of perturbative quantum chromodynamics (pQCD). Current predictions for Z +b-jets production are known at next-to-leading-order (NLO) accuracy in pQCD, and they can be derived in either a 4-flavour number scheme (4FNS) or a 5-flavour number scheme (5FNS) [1–4]. 1
Unless otherwise mentioned, it is implicitly assumed that b-quark refers to both b-quark and ¯b-antiquark.
–1–
JHEP07(2020)044
1 Introduction
2
A c-jet is a jet originating from a c-quark. ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point
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